JP5249203B2 - Polyimide film - Google Patents

Description

  The present invention relates to a polyimide film having good tear resistance and suitable as an insulating layer of a wiring board.

  In general, polyimide resin has excellent heat resistance, chemical resistance, electrical properties, and mechanical properties. Therefore, it is widely used as an electrical and electronic equipment material, especially for electrical insulation materials that require heat resistance. It's being used. Various flexible copper clad laminates having polyimide as an insulating layer have been studied so far. For example, Patent Document 1 discloses a flexible copper clad laminate made of a polyimide resin having a specific resin structure. ing. However, although conventional polyimide resin has better heat resistance and electrical insulation than other organic polymers, it has a high moisture absorption rate, so when a flexible wiring board obtained by processing this is immersed in a solder bath There were concerns such as the occurrence of blisters and poor connection of electronic equipment due to dimensional changes after moisture absorption of the polyimide resin.

  Therefore, in order to improve the dimensional stability due to changes in the humidity environment of the polyimide resin, a diamine containing 20 mol% or more of 4,4′-diamino-2,2′-dimethylbiphenyl is used as the polyimide resin for forming the polyimide resin layer. Patent Document 2 discloses a laminate having a polyimide resin layer obtained by using.

  In recent years, the performance and functionality of electronic devices have been rapidly increasing, and with this, electronic components used in electronic devices and the boards on which they are mounted have become higher density and higher performance. The demand is growing. Electronic devices are becoming lighter, smaller, and thinner, and the space for storing electronic components is becoming narrower. As one of the techniques for solving these problems, a technique for mounting a semiconductor chip on a flexible wiring board has attracted attention. The flexible wiring board used for this so-called COF (chip-on-film) application has sprocket holes for conveyance in the manufacturing process. However, this part is prone to breakage and deformation. In order to maintain the reliability, the insulating layer of the flexible wiring board up to the above requires a certain thickness of about 40 μm or more.

  On the other hand, a flexible wiring board used for a movable part such as a folding cellular phone or a sliding cellular phone is also required to have a high wiring density, and accordingly, a high bending resistance is also required. However, conventional flexible wiring boards have the problem of disconnection after a long period of use if they are multilayered or have a small bending radius, and sufficient bending resistance is provided for the movable parts of folding and sliding mobile phones. What it has was not necessarily obtained.

  As one means for improving flexibility, studies have been made to reduce the elasticity of polyimide films (Patent Document 3). Although the flexibility of the laminate is improved by lowering the elastic modulus to 3 GPa or less, there is a problem that it takes time for heat treatment to match the thermal expansion coefficient with the substrate. In addition, since COF is used for mounting at a high temperature, the polyimide having a low elastic modulus may cause the IC chip to sink at the time of mounting, which causes a defect.

  Another effective means for improving flexibility is the thinning of the polyimide, which is an insulating layer. However, the conventional polyimide film has a problem that the film is weakened by thinning, and is easily broken or deformed. Therefore, development of a polyimide film having sufficient tear resistance even in a thin film has been desired.

JP-A 63-245988 WO01 / 028767 JP 2003-192788 A

  An object of this invention is to provide the polyimide film which has the tear resistance outstanding also in the thin film, making use of the dimensional stability represented by the thermal expansion coefficient, heat resistance, and the outstanding characteristic of other polyimides.

  As a result of repeated studies to solve the above-mentioned problems, the present inventors solved the above-mentioned problems by forming a polyimide film that has a specific structure and satisfies a certain relational expression. As a result, the present invention has been completed.

ここで、Ａｒ₁は芳香環を１個以上有する４価の有機基であり、Ｒは炭素数１〜６の低級アルキル基、低級アルコキシ基、フェニル基、フェノキシ基又はハロゲンである。That is, this invention is obtained from the polyimide which contains 60 mol% or more of structural units represented by following General formula (1), is 5-40 micrometers in thickness, Formula (I)
Z = Y / X ^1.5 (I)
(In the formula, Y is a tear propagation resistance value (mN), and X is a polyimide film thickness (μm)). The value of Z is 0.7 or more and the thermal expansion coefficient is 30 ppm. It is a polyimide film characterized by being / K or less.

Here, Ar ₁ is a tetravalent organic group having one or more aromatic rings, and R is a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen.

  The present invention is described in detail below.

The polyimide film of this invention is obtained from the polyimide which contains 60 mol% or more of structural units represented by the said General formula (1). In the general formula (1), Ar ₁ is a tetravalent organic group having one or more aromatic rings, and can be said to be a residue generated from an aromatic tetracarboxylic dianhydride. Therefore, Ar ₁ is understood by describing the aromatic tetracarboxylic dianhydride used. The aromatic tetracarboxylic dianhydride used is preferably pyromellitic dianhydride, but can contain other aromatic tetracarboxylic dianhydrides in a proportion of 30 mol% or less. R is a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen. Preferably, they are a methyl group, an ethyl group, a methoxy group or an ethoxy group.

  The preferred polyimide constituting the polyimide film of the present invention contains a structural unit represented by the following general formula (2), more preferably any of the structural units represented by the following general formulas (3) and (4). Either one or both may be contained within a certain range.

In the general formula (2), R has the same meaning as R in the general formula (1). In the general formula (3), Ar ₂ represents at least one divalent aromatic group selected from the following formulas (a) and (b), and Ar ₄ is selected from the following formulas (c) and (d) And at least one of divalent aromatic groups to be produced. In the general formula (4), Ar ₃ represents a divalent residue obtained by removing an amino group from at least one diamine selected from 3,4′-diaminodiphenyl ether and 4,4′-diaminodiphenyl ether.

  In the general formulas (2), (3), and (4), l, m, and n represent the molar ratio, and when the polyimide is composed of the structural units represented by the general formulas (2) and (3), l is preferably a number in the range of 0.6 to 0.9, m is a number in the range of 0.1 to 0.4, and polyimide is a structural unit represented by the general formulas (2), (3) and (4) 1 is preferably a number in the range of 0.6 to 0.9, m is 0.09 to 0.3, and n is 0.01 to 0.2.

  The structural unit of the above general formula (2) mainly improves the properties such as low thermal expansion and high heat resistance, and the structural unit of the general formula (3) mainly improves the properties such as toughness and adhesiveness. However, it is not exact because of synergistic effects and molecular weight effects. However, in order to increase toughness and the like, it is usually effective to increase the structural unit of the general formula (3). The structural unit of the general formula (4) is effective for adjusting the balance between low thermal expansion and toughness.

Preferable examples of the structural unit represented by the general formula (2) include a structural unit represented by the following formula (5).

In General Formula (3), Ar ₂ represents a divalent aromatic group represented by the above formula (a) or (b), and Ar ₄ represents a divalent aromatic group represented by (c) or (d) above. Indicates an aromatic group. Preferred examples of Ar ₂ include divalent aromatic groups represented by the following formulas (e), (f) and (g).

In the general formula (4), Ar ₃ represents a residue of 3,4′-diaminodiphenyl ether or 4,4′-diaminodiphenyl ether (a group remaining after taking an amino group).

  The polyimide film of the present invention is preferably obtained by imidizing a polyamic acid which is a polyimide precursor having a weight average molecular weight (Mw) in the range of 150,000 to 800,000, more preferably 200,000 to 800,000. If the value of the weight average molecular weight is less than 150,000,000, the tear propagation resistance of the film tends to be weak, and if it exceeds 800,000, it may be difficult to produce a uniform film. The weight average molecular weight can be determined in terms of polystyrene by the GPC method. In addition, since the weight average molecular weight of the polyimide resin obtained by imidizing the polyamic acid is substantially equal to that measured in the polyamic acid state, the weight average molecular weight of the polyamic acid can be regarded as the weight average molecular weight of the polyimide resin. it can.

  The thickness of the polyimide film is in the range of 5 to 40 μm, preferably 5 to 35 μm, and particularly preferably 10 to 30 μm. By setting it as this range, it can be set as the polyimide film excellent in bending property and tear resistance.

  Moreover, in this invention, it is set as the polyimide film which is hard to fracture | rupture and deform | transform by making the value of Z represented by numerical formula (I) into 0.7 or more, preferably 0.9-2.5. be able to. In formula (I), Y is the tear propagation resistance value (mN), and X is the thickness (μm) of the polyimide film. The tear propagation resistance is measured by the method described in the examples.

In addition, the linear thermal expansion coefficient of the polyimide film needs to be 30 × 10 ⁻⁶ / K or less, preferably 25 × 10 ⁻⁶ / K or less, so that it can be curled when applied to a flexible wiring board. Can be suppressed.

  Furthermore, the glass transition temperature of the polyimide film is 310 ° C. or higher, preferably 310 to 500 ° C., and the elastic modulus at 400 ° C. is 0.1 GPa or higher, preferably 0.15 to 5 GPa. Therefore, it can be used for a flexible wiring board particularly suitable for COF applications or a laminate for manufacturing the flexible wiring board.

  For imidation, polyamic acid is applied onto an arbitrary substrate such as copper foil using an applicator, pre-dried at a temperature of 150 ° C. or lower for 2 to 20 minutes, and then usually 130 for solvent removal and imidization. The heat treatment is performed at a temperature of about ~ 360 ° C for about 2 to 30 minutes. The polyimide film can be obtained by removing the substrate used at the time of imidation by etching or peeling.

  The method for producing the polyimide film of the present invention is not particularly limited. For example, a polyimide precursor (polyamic acid) resin solution, which is a raw material of the polyimide film, is cast on an arbitrary support substrate. After forming into a film and heating and drying on a support to form a gel film having a self-supporting property, it is generally peeled off from the support and then heat-treated at a high temperature to be imidized to form a polyimide film. Is. Polyamic acid is cast-applied on an arbitrary substrate such as copper foil using an applicator, pre-dried, and then heat-treated for solvent removal and imidization, and the substrate used during imidation is peeled off. Or the method of removing by etching etc. is also mentioned. At this time, it is appropriate that the drying condition is 150 ° C. or lower for 2 to 30 minutes, and the heat treatment for imidization is performed at a temperature of about 130 to 360 ° C. for about 2 to 30 minutes.

  The polyamic acid used as the raw material of the polyimide film can be produced by a known method of polymerizing in an organic polar solvent using substantially equimolar amounts of aromatic diamine and aromatic tetracarboxylic dianhydride. That is, it is obtained by dissolving an aromatic diamine in an organic polar solvent such as N, N-dimethylacetamide under a nitrogen stream, adding aromatic tetracarboxylic dianhydride, and reacting at room temperature for about 3 to 5 hours. It is done. The aromatic diamine and aromatic tetracarboxylic acid used as the raw material can be understood from the explanations of the general formulas (2), (3) and (4), but specific examples include 2,2′- Dimethylbenzidine (m-TB), 1,3-bis (4-aminophenoxy) benzene (TPE-R), 3,4'-diaminodiphenyl ether (3,4'-DAPE), etc., aromatic tetracarboxylic acid An example of a dianhydride is pyromellitic dianhydride (PMDA).

  The polyimide film of the present invention is suitable as an insulating layer of a laminate (CCL) for a flexible wiring board. A flexible printed circuit board (FPC) can be manufactured by etching a metal layer of CCL into a circuit pattern. CCL has a metal layer on one or both sides of an insulating layer, and the insulating layer is composed of a polyimide layer or a layer mainly composed of a polyimide layer. The polyimide layer contains 50% or more, preferably 70 to 95% of the thickness of the polyimide film of the present invention.

Hereinafter, the content of the present invention will be specifically described based on examples, but the present invention is not limited to the scope of these examples.
Abbreviations used in Examples and the like are shown below.
• PMDA: pyromellitic dianhydride • TPE-R: 1,3-bis (4-aminophenoxy) benzene • APB: 1,3-bis (3-aminophenoxy) benzene • m-TB: 2,2 ' -Dimethylbenzidine, 3,4'-DAPE: 3,4'-diaminodiphenyl ether, MABA: 4-amino-N- (4-amino-2-methoxyphenyl) -benzamide, DMAc: N, N-dimethylacetamide

  In addition, measurement methods and conditions for various physical properties in the examples are shown below. In addition, what was expressed as a polyimide film below refers to the polyimide film obtained by carrying out the etching removal of the copper foil of the laminated body which used copper foil as a support base.

Measurement of Tear Propagation Resistance (TDR):
A 63.5 mm × 50 mm test piece was prepared from the polyimide film, a 12.7 mm long cut was made into the test piece, and measurement was performed in accordance with ASTM D1922 using a light load tear tester manufactured by Toyo Seiki.

Measurement of coefficient of thermal expansion (CTE):
The polyimide film (3 mm × 15 mm) was subjected to a tensile test in a temperature range of 30 ° C. to 260 ° C. at a constant temperature increase rate while applying a 5.0 g load with a thermomechanical analysis (TMA) apparatus. The thermal expansion coefficient was measured from the amount of elongation of the polyimide film with respect to temperature.

Glass transition temperature (Tg), storage modulus (E ′):
The dynamic viscoelasticity when a polyimide film (10 mm × 22.6 mm) was heated from 20 ° C. to 500 ° C. at a rate of 5 ° C./min was measured by DMA. The storage elastic modulus (E ′) of was determined.

Synthesis Examples 1-6
In order to synthesize polyamic acids (polyimide precursor resins) A to F, the diamines shown in Table 1 were dissolved in about 200 to 300 g of solvent DMAc while stirring in a 500 ml separable flask under a nitrogen stream. Subsequently, the tetracarboxylic dianhydride shown in Table 1 was added. Thereafter, the solution was stirred at room temperature for 4 hours to carry out a polymerization reaction to obtain a yellow-brown viscous solution of polyimide precursor resins A to F. The viscosity of each polyamic acid resin solution at 25 ° C. was measured and summarized in Table 1.

  The viscosity was measured at 25 ° C. with a cone plate viscometer (manufactured by Tokimec Co., Ltd.) equipped with a constant temperature water bath. Table 1 shows the weight average molecular weight (Mw) measured by GPC. In Table 1, the unit of the amount of diamine and tetracarboxylic dianhydride used is g.

Examples 1-4
After applying the solution of A to D polyamic acid on an electrolytic copper foil (surface roughness Rz: 0.7 μm) each having a thickness of 12 μm using an applicator and drying at 50 to 130 ° C. for 2 to 60 minutes Further, stepwise heat treatment is performed at 130 ° C., 160 ° C., 200 ° C., 230 ° C., 280 ° C., 320 ° C. and 360 ° C. for 2 to 30 minutes each to form a polyimide layer on the copper foil, thereby obtaining a laminate. It was.

Etching away the copper foil of the laminate using ferric chloride aqueous solution to create polyimide films AD, tear propagation resistance, thermal expansion coefficient (CTE), glass transition temperature (Tg), storage at 400 ° C The elastic modulus (E ′) was determined. The results are shown in Table 2.
In addition, the polyimide films A to D mean that they were obtained from the corresponding polyamic acids A to D.

Comparative Examples 1 and 2
Polyimide films E and F were prepared in the same manner as in Example 1 except that E and F were used as the polyamic acid, and the physical properties were measured. Table 2 shows the characteristics of the polyimide films E and F.

Examples 5-8
The solution of polyamic acid D was applied onto an electrolytic copper foil having a thickness of 12 μm (surface roughness Rz: 0.7 μm) using an applicator while changing the thickness in each example, and the solution was applied at 50 to 130 ° C. for 2 to 60 After drying for a minute, further heat treatment is performed at 130 ° C., 160 ° C., 200 ° C., 230 ° C., 280 ° C., 320 ° C., 360 ° C. for 2-30 minutes each, and the thickness of the copper foil is as shown in Table 3 A laminate having a polyimide resin layer formed thereon was obtained.
The copper foil was etched away using a ferric chloride aqueous solution to prepare polyimide films G to J, and the tear propagation resistance and the coefficient of thermal expansion (CTE) were determined. The results are shown in Table 3.

Industrial applicability

  The polyimide film of the present invention not only has excellent dimensional stability and heat resistance, but also has good tear resistance, so that the thickness can be reduced, and an FPC insulating layer or sprocket used in a bent part of a mobile phone. Suitable for COF insulating layer having holes.

Claims (2)

It is obtained from a polyimide containing a structural unit represented by the following general formula (2) and a structural unit represented by the following general formulas (3) and (4), has a thickness of 5 to 40 μm, and a thermal expansion coefficient of 30 ppm. / K or less, when the tear propagation resistance value (mN) is Y and the thickness (μm) of the polyimide film is X, Formula (I)
Z = Y / X ^1.5 (I)
A polyimide film characterized in that the value of Z calculated in (1) is 0.7 or more.

In General formula (2), R is a C1-C6 lower alkyl group, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen. In the general formula (3), Ar ₂ represents at least one divalent aromatic group selected from the above formulas (a) and (b), and Ar ₄ is selected from the above formulas (c) and (d). And at least one kind of divalent aromatic group to be produced. In the general formula (4), Ar ₃ represents a divalent residue obtained by removing an amino group from at least one diamine selected from 3,4′-diaminodiphenyl ether and 4,4′-diaminodiphenyl ether. In the general formulas (2), (3), and (4), l, m, and n represent the molar ratio, l is 0.6 to 0.9, m is 0.09 to 0.3, n Is a number in the range of 0.01 to 0.2.

  The polyimide film according to claim 1, wherein the glass transition temperature is 310 ° C or higher and the elastic modulus at 400 ° C is 0.1 GPa or higher.